The art of rod cutting has produced both hand held and bench mounted tools. These tools are capable of cutting a wide variety of rod strengths and thicknesses, ranging from wire to hardened steel rod. Thus, a tool can be made to cut almost any workpiece. However, the quality of the cut and the characteristics of the tool are subject to wide variation. An area having extremely difficult requirements is surgery. Here, the tool must be made with sufficient clearances to permit sterilization, but the workpiece frequently is extremely tough surgical steel. In addition, the accuracy requirement may be extremely rigid, as the rod being cut is being custom fitted into a patient in the normal course of a surgical procedure.
According to present practice in the art, surgeons have employed the well known bolt cutter having compound levers and pivoted jaws, which has a combination of strength, mechanical advantage, and looseness of parts to permit its use in an operating room. This tool also has several notable disadvantages. A very notable one is that a bolt cutter leaves the cut end of a cut rod with a rough, wedge shaped tip, which is very undesirable as a long term fixture in the human body. Further, due to the extreme hardness of some surgical steel rods, the bolt cutter can be extremely difficult to use and may lead to muscle damage and hernia in the user. Still another problem is that a bolt cutter snaps off the end of the workpiece, which has been known to fly through the air with considerable force and cause damage.
Among other known designs for rod or bolt cutters is the teachings of U.S. Pat. No. 54,520, wherein a tool housing carries both a cap plate and an opposed cutter disk with matching bores located over the faces of the disc and cap plate, but generally around the circumferential area. A wire or rod is inserted through the common bores and the cutter disk is rotated with respect to the cap plate in order to cut the workpiece. An advantage of this arrangement is that there is no center pin on which the plates rotate. Thus, the size of rod that the cutter can sever is not limited by the size of a center pin, which would be in danger of breaking before such large rod is cut. However, it is notable that the matching bores are considerably offset radially outwardly from the typical location for a center pin, if such were to be present.
Another cutter is shown in U.S. Pat. No. 2,560,318 wherein a tool has multiple holes to allow different gage wire or bolts to be cut in a pivoting cutting action about a center pin. The holes typically are offset by a considerable radial distance from the center pin. Other tools having a center pivot pin are shown in U.S. Pat. Nos. 2,494,996, 3,333,338, and 3,370,353. In these, also, the cutting holes are radially spaced from the center pin by a substantial distance. In addition, the tools of the latter three patents appear to be hand held tools that are portable enough to be placed in a sterilizer.
Further examples of the state of the art appear in U.S. Pat. No. 2,249,515, which discloses a simple pivoted shear; U.S. Pat. No. 2,543,018, which discloses a combination of a disk with rod supporting holes and a cutting blade that operates against the disk; and U.S. Pat. No. 4,722,257, which discloses bench mounted bolt cutter. These tools employ scissors style shearing action, in which the work site is in progressive motion along the closing blades.
It would be desirable to have a rod cutter that is adapted to the specific requirements of an operating room where, as noted above, the workpiece rods are of especially hard steel. Also, it would be desirable to have a rod cutter that operates by shearing action with an applied rotary torque or wringing action, so that the surgical steel rods are sheared with added ease and with an excellent smoothness on the cut end. A bench mounted cutter could offer still better ease of use and less chance of injury to the user, but any cutter of bench size would have to be of a size to accommodate sterilization requirements. Further, the construction of the rod cutter should permit space to be left between moving parts so that all parts can be sterilized.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the rod cutter of this invention may comprise the following.